1. Field of the Invention
The present invention relates to methods and systems for removing technetium from streams of material. More specifically, this invention relates to methods and systems for removing technetium of varying valences.
2. Description of the Related Art
The prior art discloses that technetium ("Tc") is a difficult material to remove from environmental and process discharge streams, including those of hydrometallurgical processing operations, because of the facts that: 1) Tc exists in multiple, stable valence states; and 2) Tc can change valence states when exposed to relatively mild oxidizing or reducing conditions relatively easily in comparison to other transition metals. See R. E. Wildung, L. M. McFadden, and T. R. Garland, "Technetium Sources and Behavior in the Environment," J. Environ. Qual., Vol. 8, no. 2, p. 156 (1979), incorporated herein by reference.
The prior art discloses using a solvent extraction/resin adsorption/ion exchange/crystallization method to remove the Tc. However, the Tc valence variations inhibit the necessary solvent extraction and/or resin adsorption efficiencies to reduce the Tc percentage in the stream to desired levels. The Tc valences can be controlled to an extent using relatively large additions of chemicals to adjust the pH, oxidation, or both. This results in increased removal processing costs and an increased secondary waste volume to process for disposal. Further, the repeated regeneration of the extraction resin is costly in itself, with the efficiency of the resin decreasing with each regeneration cycle. See Dow Chemical U.S.A., "Demineralization of Organically Contaminated Waters," Idea.+-.Exchange, Vol. 8, No. 1.; and Rohm and Haas Company, Fluid Process Chemicals Department, "Recovery of Precious Metals with Amberlite Ion Exchange Resins," Amber-Hi-Lites, No. 171 (Autumn 1982), both of which are incorporated herein by reference.
Therefore a need exists to provide an efficient Tc removal method and system which is robust enough to remove Tc of various valences.